Optical networks are found in a wide variety of high speed applications, and used to provide efficient transmission of voice, video and data signals. Some optical networks implement wavelength division multiplexing (WDM) to increase network bandwidth. In WDM optical networks, multiple optical channels occupying distinct wavelengths/frequencies are multiplexed into a single optical signal for transmission through a single optical fiber.
Error rates in long-haul WDM optical networks depend on, among other things, per channel optical power and optical signal-to-noise ratio (OSNR) values. Modules such as optical amplifiers have been found to degrade the OSNR, as well as produce power ripple across the optical band for the transmission channels. To remedy these problems, WDM optical networks often implement systems that perform optical channel power monitoring and/or optical channel power correction to maintain optimal channel powers and desired low error rates.
Various types of optical channel monitors (OCMs) have been developed to perform these functions, and in general are configured to measure the multiple wavelengths used within a WDM network, with OCMs disposed at various locations throughout the network. The power level of each optical channel may be reported in real time, with feedback from the OCM to a “host” (such as a Network Management System (NMS)) utilized to optimize the optical power level for each channel, identify performance drift, and verify system functionality.
More complex networks may use dense WDM (DWDM) systems, which support the communication of a large number of separate optical fibers (ports), each port supporting multiple optical channels. Monitoring equipment for these DWDM systems becomes increasingly expensive and time-consuming to use, requiring multiple measurements of each signal as they pass through many optical elements in the system. Additionally, one or more of the signals appearing at a monitoring arrangement may be of relatively low power, making it difficult to accurately measure the signal level in the presence of the noise created within the measurement system itself.